1. Field of the Invention
The present invention relates to a motor shaft for a rotational-to-direct motion converting motor which is, for example, used for a valve (EGR-V) of an exhaust gas re-circulation system and has a mechanism for converting a rotational motion of a valve motor into a reciprocating motion (or a direct driving motion). Also, the present invention relates to a method of manufacturing the motor shaft.
2. Description of Related Art
As is disclosed in the Published Unexamined Japanese Patent Application H7-27023 (1995), an apparatus for controlling an exhaust gas re-circulation control valve (EGR-V) has been known as a prior art. In this control apparatus, a rotational motion in a stepping motor (or a linear motor) is converted into a linear motion, the EGR-V is driven, a valve opening is adjusted, and a flow rate of a re-circulated exhaust gas is adjusted. Also, a pushing type control valve, in which a motor shaft pushes a valve shaft to open a valve, and a lifting type control valve, in which a motor shaft pulls a valve shaft to open a valve, are disclosed in the Application.
Also, in the Published Unexamined Japanese Patent Application H8-49782 (1996), a technique, in which a compression molding is performed while arranging a non-protruding end of a screw shaft between metal molds, is disclosed as a processing method in the Application. Also, in the disclosure of the Application, the use of another processing method is allowed on condition that no flash is produced on a surface of an engaging-protruding portion in the processing method. Also, a mechanism, in which a motor shaft and a valve-shaft are integrally formed with each other to fix a valve to an end portion of the motor shaft, is disclosed.
In addition, in the Published Unexamined Japanese Patent Application H10-215545 (1998), a technique, in which a round bar is formed into a motor shaft by grinding the round bar with a finishing machine, and a technique, in which a motor shaft is molded according to a metal injection molding method, are disclosed. Also, a technique, in which a screw portion is formed according to a form rolling method, a rotation regulating portion adapted to a phase (or lead and pitch) of the screw portion is formed according to a resin inserting molding or a metal injection molding and the rotation regulating portion and the screw portion are welded together to form a motor shaft, is disclosed.
Here, a structure of a general EGR-V is described.
FIG. 1 is an internal structural diagram of a stepper motor driving type exhaust gas re-circulation control valve which denotes a motor-driven control valve apparatus and in which a stepper motor is used as a motor.
In FIG. 1, a housing 1 has an input port 2 leading to an exhaust system of an engine, an output port 3 leading to an intake system of the engine, a pair of reflux passages 4a and 4b, and a water-cooling passage 14 for cooling the motor and a valve body. A valve seat 6 is inserted into the reflux passage 4a under pressure, and a roll pin 13 prevents the valve seat 6 from coming out from the reflux passage 4a. 9 indicates a bush functioning as a bearing. 8 indicates a holder which prevents deposits from penetrating into the bush 9. The holder 8 is arranged with the valve seat 6 on the same axis and is placed between the housing 1 and the valve seat 6.
5 indicates a valve which is arranged to come in contact with the valve seat 6. The valve 5 is fixed to a valve shaft 7 at caulking structure. The valve shaft 7 penetrates through the bush 9, a spring holder A10 and a washer 13 are fixed to the valve shaft 7 at caulking structure on the opposite side to the valve 5. 12 indicates a spring A which is arranged between the spring holder A10 and the housing 1 at a contracted form so as to give a power to the valve 5 in a valve-close direction.
20 indicates a stepper motor. An attaching screw 46 attaches the stepper motor 20 to the housing 1 so as to make an axis center of the stepper motor 20 agree with that of the housing 1. 22 indicates a pair of bobbins. A coil 23 is wound on each bobbin 22. A yoke A24 and a yoke B25 functioning as a magnetic path are arranged on the outer periphery of each bobbin 22. 29 indicates a terminal electrically connected with the coils 23. A connector is formed of the terminal 29 and a motor housing 21. 27 indicates a plate A magnetically shielding one coil portion from the other coil portion. 26 indicates a plate B which prevents resin from flowing into the inner peripheries of the coil portions when the motor housing 21 is formed.
31 indicates a magnet. 32 indicates a rotor having the magnet 31. A screw portion 32a and a stopper portion 32b for stopping the movement of a motor shaft 70 in a longitudinal direction are arranged in the inner periphery of the rotor 32. The screw portion 32a is screwed to a screw portion 70a of the motor shaft 70. 30 indicates a pair of bearings attached to both ends of the rotor 32. 28 indicates a plate spring generating a side pressure given to the bearings 30. 70 indicates the motor shaft having the screw portion 70a. The screw portion 70a is screwed to the screw portion 32a so as to make the motor shaft 70 perform a reciprocating motion, so that a rotational motion performed in the rotor 32 is converted into a linear motion of the motor shaft 70. 34 indicates a stopper pin inserted into the motor shaft 70 under pressure. 41 indicates a motor bush having a bearing function and a rotation preventing function for preventing the rotational motion of the motor shaft 70. The rotation preventing function is generated by a hole of the motor bush 41 having a D form at cross section.40 indicates a motor holder having the same center as that of the motor housing 21. The motor holder 40 is arranged between the motor housing 21 and the housing 1 and holds the bearings 30 and the motor bush 41.
In the motor having the above configuration, in a valve opening operation, the rotor 32 including the magnet 31 is rotated in a valve-open direction step by step according to a pulse-shaped voltage signal which is sent from a control unit (not shown) to the terminal 29. In this case, the number of transmitted pulses agrees with the number of stepped motions of the rotor 32, so that an open loop control can be correctly performed. This step-by-step rotation of the rotor 32 is transmitted to the motor shaft 70 through the screw portion 32a of the rotor 32 and the screw portion 70a of the motor shaft 70. Because a rotational motion in the motor shaft 70 is prevented by both a D portion 70b of the motor shaft 70 having a semi-circular shape at cross section and a D hole of the bush 41, the rotational motion of the rotor 32 is converted into a linear motion of the motor shaft 70, and the motor shaft 70 is moved in a valve-open direction (that is, in the lower direction in FIG. 1).
Because a conventional motor shaft for a rotational-to-direct motion converting motor has the above configuration, it is difficult to perform the positioning of the motor shaft 70 in the form rolling, and there is a case where the screw portion is not correctly positioned.
Also, a rotation stopping portion (that is, the D portion 70b) of the motor shaft 70 is made of a material other than that of the motor shaft 70 to adapt the phase of one screw portion 32a to that of the other screw portion 70a, and one screw portion 70a is fixed to the rotation stopping portion to make the phase of the screw portion 70a agree with that of the rotation stopping portion. Therefore, there is a problem that the number of parts of the motor shaft 70 is increased and the processing procedure for the motor shaft 70 is complicated.
In addition, in the manufacturing method of the conventional motor shaft 70, because a round bar is formed into the conventional motor shaft 70 by grinding the round bar, a portion of the round bar removed in the grinding operation is drawn off as scrap metal. Therefore, there is another problem that an useless portion of the round bar removed as scrap metal is increased.
In particular, in cases where the rotation stopping portion of the motor shaft 70 is made of the same material as that of the motor shaft 70, it is required to form a round bar having a larger diameter into a motor shaft Therefore, an useless portion of the round bar is moreover increased.
The present invention is provided to solve the above problems, and an object of the present invention is to provide a motor shaft for a rotational-to-direct motion converting motor in which the positioning in a form rolling operation is easily performed and in which phases of screws connected to each other are easily adapted to each other.
Also, the object of the present invention is to provide a method of manufacturing the motor shaft in which a material of the motor shaft is efficiently used.
A manufacturing method of a motor shaft for a rotational-to-direct motion converting motor according to the present invention comprises a step for forming an end portion of a wire rod into a large diameter portion, a step for flattening the large diameter portion to form the large diameter portion into a plate portion having a prescribed thickness, a step for taking out a prescribed-shaped rotation stopping portion from the plate portion having the prescribed thickness, and a step for forming thread ridges on the wire rod other than the rotation stopping portion. Because the rotation stopping portion is formed after the wire rod is once formed into the large diameter portion, a diameter of the wire rod can be reduced.
Also, a manufacturing method of a motor shaft for a rotational-to-direct motion converting motor according to the present invention comprises a step for taking out a prescribed-shaped second plate material including a rotation stopping portion from a first plate material, a step for forming the second plate material other than the rotation stopping portion into a columnar portion by pressing the second plate material, and a step for forming thread ridges on the columnar portion. Because the thread ridges is formed after the second plate material is once formed into the columnar portion, the first plate material can be thinned.
Also, the step for forming thread ridges in the manufacturing method comprises a step for forming the thread ridges according to a form rolling. Therefore, the thread ridges can be rapidly formed.
Also, a motor shaft for a rotational-to-direct motion converting motor comprises a rotation stopping portion formed in a plate shape, a screw portion formed in a columnar shape, and a hole, arranged in an end portion of a motor shaft in a longitudinal direction, for positioning the motor shaft in a form rolling. Therefore, a position shift or a phase shift of the thread ridges formed on the screw portion can be prevented.